As disclosed in U.S. Pat. No. 4,590,010 (Ramachandran et al. I), it is known that 6-alkoxy-5-halo-1-cyanonaphthalenes are useful as pharmaceutical intermediates and that they can be prepared by (1) reacting a 6-alkoxytetralone with cyanide ion and a Lewis acid in a suitable solvent, such as nitrobenzene, to cyanate it to a 6-alkoxy-1-cyano-3,4-dihydronaphthalene, (2) aromatizing the resultant 6-alkoxy-1-cyano-3,4-dihydronaphthalene, preferably by dehydrogenation in the presence of a palladium-on-carbon catalyst, (3) isolating the resultant 6-alkoxy-1-cyanonaphthalene, and (4) halogenating it in a suitable solvent, such as a halogenated alkane. This process, although generally satisfactory, is somewhat inconvenient because of the number of steps required to isolate the 6-alkoxy-1-cyanonaphthalene for halogenation.
Copending application Ser. No. 880,070 (Ramachandran et al. II), filed June 30, 1986, teaches that a 6-alkoxy-1-cyano-3,4-dihydronaphthalene can be aromatized by intimately mixing it with a base selected from alkali metal, alkaline earth metal, and tetraalkylammonium hydroxides, alkoxides, carbonates, and bicarbonates in the presence of a hydrogen acceptor, such as nitrobenzene. The use of nitrobenzene in the reaction has the disadvantage of leading to the formation of azoxybenzene, a compound which is difficult to separate from the 6-alkoxy-1-cyanonaphthalene.